A gear pump uses the meshing of gear wheels (gears) to pump fluid through fluid displacement. Gear pumps are one of the most common types of pumps for hydraulic applications. For example, oil pumps used in internal combustion engines are usually implemented as gear pumps. Gear pumps are also widely used in chemical installations to pump highly viscous fluids. Basically, two different types of gear pumps exist, i.e. external gear pumps, which use two external spur gears, and internal gear pumps, which use an external spur gear and an internal spur gear.
As the gears rotate, the gear teeth come out of mesh on the intake side (suction side) of the pump thereby creating a void and respective suction. The void is filled by fluid, which is carried by the gears to the outlet side (pressure side) of the pump, where the meshing of the gears displaces the fluid. The mechanical clearances are small (on the order of a few 10 micrometers), and the tight clearances, along with the speed of rotation, effectively prevent the fluid from leaking back. Usually, the rigid design of the gears and the housing allows for very high pressures and the ability to pump highly viscous fluids.
External gear pumps are usually designed such that, on the intake side, the fluid (e.g. oil) flows towards the gears in a radial direction (radial inflow). In this regard the terms “radial” and “axial” refer to the rotation of the gears. Particularly when two engaged teeth of two meshed gears are about to come out of the mesh at the intake side of the pump, the above-mentioned void does not yet have a radial connection to the intake channel and path of the fluid is still blocked by the teeth of the gears. At the same time the volume between the two meshed teeth (not yet filled with fluid) becomes larger, which leads to a drop of pressure in this volume. When the two teeth finally disengage, the radial connection between the above-mentioned void and the intake suddenly opens, which may lead to an abrupt increase of local pressure and, in the worst case, to cavitation. The resulting pressure variations may impede the fluid flow into the void, deteriorate the volumetric efficiency of the pump, and increase undesired leakage. In particular, the sudden pressure drops of the opening teeth may suck oil through the small sealing gap (clearance seal) from the pressure side of the pump, which gives rise to additional leakage.
In view of the above explanation, one object of the present disclosure may be to provide a gear pump with improved efficiency. This object as achieved by the gear pump of claim 1. Various embodiments and further developments are covered by the dependent claims.